Microcellular foaming

Microcellular foams refer to thermoplastic foams with cells of the order of 10 μm in size. Typically these foams are rigid, closed-cell structures; although recently there is much interestin creating open-cell, porous structures that have cells in this size range. The microcellular process that sparked the growthin this field over the past three decades was invented at Massachusetts Institute of Technology, USA, in early eighties [1], in response to a challenge by food and film packaging companies to reduce the amount of polymer used in their industries. As most of these applications used solid, thinwalledplastics, reducing their densities by traditional foaming processes that produced bubbles larger than 0.25 mm was notfeasible due to excessive loss of strength. Thus was born the idea to create microcellular foam [2], where we could have, for example, 100 bubbles across one mm thickness, andexpect to have a reasonable strength for the intended applications. There are several approaches to achieving microcellular foam.Use of supercritical blowing agent, nanoparticle [3]. shear rate, Elastomer particles and improve of foaming conditions such as stabilization temperature and pressure drop rate are some of these approaches [4]. The solid-state microcellular process, high pressure vessel process, semi-continuous process such as injection molding), extrusion and other processing methods are several ways to make microcellular plastics [4].